The present invention generally relates to an electrical resonator and more particularly, to a dielectric resonator employing TM.sub.010 mode or its variation mode for electromagnetic waves.
The construction of the dielectric resonator of this kind in terms of principle has already been known, and there are various problems to be solved for the actual applications, one of which problems is related to a resonant frequency adjusting construction, which are conventionally disclosed, for example, in Japanese Utility Model Laid-Open Publications Jikkaisho No. 59-57005 and No. 59-88908, and so arranged as shown in FIG. 1, that a frequency adjusting member 4 made of a metal or dielectric member is inserted into a space 3 defined between an inner peripheral surface of a metallic case 2 closed at its opposite ends and a columnar inner dielectric member 1 disposed at a central portion within said case 2. The frequency adjusting member 4 made of a metal is not suitable for actual application, since a loss tends to be large. In the case where the frequency adjusting member 4 is of a dielectric material, it is assumed that the resonant frequency is altered through variation of a capacitance value in an equivalent circuit when the resonant frequency of the resonator is to be considered. However, in the known construction as referred to above, since the frequency adjusting member 4 is located at a place where the density of electric lines of force is low, the resonant frequency can not be effectively altered. Moreover, due to the fact that the capacitance considered between the frequency adjusting member 4 and the surface of the metallic case 2 confronting said frequency adjusting member 4 on an extension line thereof, is small as compared with the capacitance of the frequency adjusting member itself, values of such capacitances are not much altered even when the adjusting member 4 is moved to a large extent upon consideration of a combined capacitance, and it has been impossible to effectively alter resonant frequencies by the known constructions.
By way of example, when the resonant frequency was represented by fo and frequency variable range was denoted by .DELTA.f, the only relation obtainable was EQU .DELTA.f/fo.ltoreq.0.2%.
If it is intended to obtain the frequency variable range larger than the above, unloaded Q factor (=Qo) is undesirably lowered to a large extent. For example, on the assumption that the range of lowering of the unloaded Q factor (=Qo) is represented by .DELTA.Qo, the resultant relation would undesirably be EQU .DELTA.Q/Qo.gtoreq.10%.
This is considered to be attributable to the fact that, owing to the construction, the current is concentrated upon the resonant frequency adjusting mechanism and a loss is produced by a contact resistance thereof.